1. Field of the Invention
The present invention relates to the field of semiconductor devices, and more particularly, to a photodiode deivce in dielectrically isolated and silicon-on-insulator structures having improved photo-carrier collection efficiency.
2. Related Art
Optically coupled solid state relays, such as those used in telecommunications signalling, use a light emitting diode (LED) and a stack of photodiodes to control a high-voltage switch. Several conventional approaches to solid-state relays are discussed by J.C. Gammel in an article titled, "High-Voltage Solid State Relays for Telecommunications" (Electro, Section 24, pp. 1-4, 1986).
The LEDs commonly used in solid state relays emit light in or near the infra-red region of the electromagnetic spectrum. Infra-red light of this wavelength penetrates the silicon to a depth of between 30-60 micrometers. The efficiency of the photodiode, which is primarily determined by the short-circuit current under illumination is a critical parameter. The efficiency of the photodiode determines the silicon area required to provide a specific drive capability for the high-voltage switch of the solid-state relay.
In accordance with the design criteria of nearly all solid-state devices, what is desired is a photodiode structure with an improved drive capability which minimizes the silicon area required to implement such a device.